Various standards allow remote stations, such as portable computers, to be moved within a wireless local area network (WLAN) and connect via radio frequency (RF) transmissions to an access point (AP) that is connected to a wired network. The wired network is often referred to as a distribution system. The various standards include the IEEE 802.11 standard and its corresponding letter revisions thereof, such as 802.11b and 802.11g, for example.
A physical layer in the remote stations and in the access point provides low level transmissions by which the stations and the access point communicate. Above the physical layer is a media access control (MAC) layer that provides services, such as authentication, deauthentication, privacy, association and disassociation, for example.
In operation, when a remote station comes on-line, a connection is first established between the physical layers in the station and the access point. The MAC layers can then connect. Typically, for the remote stations and the access point, the physical layer RF signals are transmitted and received using monopole antennas.
A monopole antenna radiates in all directions, generally in a horizontal plane for a vertically oriented element. Monopole antennas are susceptible to effects that degrade the quality of communication between the remote station and the access point, such as reflection or diffraction of radio wave signals caused by intervening objects. Intervening objects include walls, desks and people, for example. These objects create multi-path, normal statistical fading, Rayleigh fading, and so forth. As a result, efforts have been made to mitigate signal degradation caused by these effects.
One technique for counteracting the degradation of RF signals is to use two antennas to provide diversity. The two antennas are coupled to an antenna diversity switch in one or both of the remote stations and the access point. The theory behind using two antennas for antenna diversity is that, at any given time, at least one of the antennas is likely receiving a signal that is not suffering from the effects of multi-path. Consequently, this antenna is the antenna that the remote station or access point selects via the antenna diversity switch for transmitting/receiving signals. Nonetheless, there is still a need to address the degradation of RF signals between the remote stations and an access point in a wireless local area network.
In addition, another problem arises when a remote station is not aware that the access point and a selected remote station are communicating with one another, and this remote station attempts to communicate with the access point. As a result, collisions occur at the access point. This leads to a situation called the hidden node problem, which is due to the fact that not every remote station in a wireless local area network is able to communicate directly with every other remote station in the network.